#include<iostream>
using namespace std;
class Solution {
public:
    char dismantlingAction(string arr) {
        int hash[26] = { 0 };
        int n = arr.size();
        for (int i = 0; i < n; i++)
            hash[arr[i] - 'a']++;
        for (int i = 0; i < n; i++) {
            if (hash[arr[i] - 'a'] == 1)return arr[i];
        }
        return ' ';
    }
};